1. Field of the Invention
The invention relates to a mobile wireless communication terminal, a method of matching an antenna in a mobile wireless communication terminal, and a program causing a computer to carry out the method.
2. Description of the Related Art
A mobile wireless communication terminal such as a mobile phone is generally designed to include a circuit for transmitting signals and a circuit for receiving signals.
FIG. 1 is a block diagram of a conventional circuit 1000 for transmitting and receiving signals. The circuit 1000 is equipped in a mobile phone.
As illustrated in FIG. 1, the conventional circuit 1000 includes a main antenna 10 and a subsidiary antenna 9. The main antenna 10 is mainly used, and the subsidiary antenna 9 is subsidiarily used.
A capacitor 11 is electrically connected at one end to the main antenna 10, and at the other end grounded. Similarly, an inductor 12 is electrically connected at one end to the main antenna 10, and at the other end grounded. The capacitor 11 and the inductor 12 match the main antenna 10.
A capacitor 8 is electrically connected at one end to the subsidiary antenna 9, and at the other end grounded. Similarly, an inductor 7 is electrically connected at one end to the subsidiary antenna 9, and at the other end grounded. The capacitor 8 and the inductor 7 match the subsidiary antenna 9.
Which antenna is used among the main and subsidiary antennas 10 and 9 is determined by a switch 6. Specifically, if the subsidiary antenna 9 is electrically connected to a later mentioned duplexer 5 through the switch 6, the subsidiary antenna 9 is in usable condition, and if the main antenna 10 is electrically connected to the duplexer 5 through the switch 6, the main antenna 10 is in usable condition.
The circuit 1000 further includes a radio-frequency integrated circuit (RFIC) 1 for modulating signals to be transmitted and extracting base band signals out of received signals, an analog base band (ABB) 16 receiving base band signals from the RFIC 1 and transmitting base band signals to the RFIC 1, and a temperature-compensated crystal oscillator (TCXO) 15 generating a reference frequency and transmitting the thus generated reference frequency to the RFIC 1.
The RFIC 1 includes a phase-locked loop (PLL) synthesizer 1a used in signal transmission, a voltage-controlled oscillator (VCO) 1b used in signal transmission, a mixer 1c used in signal transmission, a phase-locked loop (PLL) synthesizer 1d used in signal receipt, a voltage-controlled oscillator (VCO) 1e used in signal receipt, and a mixer 1f used in signal receipt.
The PLL synthesizer 1a and the VCO 1b transmit carrier waves in accordance with a reference frequency received from the TCXO 15. The mixer 1c modulates signals in accordance with both the carrier waves received from the VCO 1b and base band signals received from the ABB 16.
The circuit 1000 further includes a band pass filter 2 which allows signals having frequencies necessary for signal transmission among modulated signals received from the mixer 1c to pass therethrough, an amplifier 3 for amplifying the signals having passed the band pass filter 2, and an isolator 4 through which the signals having been amplified by the amplifier 3 are transmitted to a duplexer 5. The isolator 4 prevents signals to be transmitted to a signal-receipt circuit from being transmitted to a signal-transmission circuit.
The duplexer 5 provides signals having frequencies belonging to a signal-transmission band among signals received from the amplifier 3 through the isolator 4, to either the main antenna 10 or the subsidiary antenna 9 through the switch 6, and further provides signals having frequencies belonging to a signal-receipt band among signals received through the main antenna 10 and the subsidiary antenna 9, to a signal-receipt circuit including a low-noise amplifier 13 and a band pass filter 14 (both mentioned later).
The circuit 1000 further includes a low-noise amplifier 13 which amplifies signals received from the duplexer 5, and a band pass filter 14 which allows signals having frequencies belonging to a signal-receipt band among signals having been amplified by the low-noise amplifier 13, to pass the re through.
The PLL synthesizer id and the VCO 1e transmit local signals in accordance with a reference frequency received from the TCXO 15. The mixer if extracts base band signals out of signals received from the band pass filter 14, in accordance with the local signals received from the VCO 1e, and transmits the thus extracted base band signals to the ABB 16.
A path through which a signal to be transmitted runs and a path through which received signal runs are generally matched to have a resistance of 50 ohms, for instance, in order to maximize a power to be transmitted to loads.
In FIG. 1, in order to avoid complexity, the capacitors 8 and 11 and the inductors 7 and 12 are illustrated only in the vicinity of the antennas 9 and 10. However, it should be noted that other capacitors and inductors are actually arranged on other paths.
For instance, a circuit including a plurality of antennas such as the above-mentioned antenna 1000 is suggested in Japanese Patent Application Publications Nos. 7-147601 and 2001-111463. A mobile phone including a circuit for matching an impedance is suggested in Japanese Patent Application Publications Nos. 2001-345882, 2001-274652, and 2002-152078.
The conventional mobile wireless communication terminal is accompanied with a problem that, as illustrated in FIG. 2, a return loss and hence a signal-receipt sensitivity varies in dependence on a circumstance of the terminal. For instance, a return loss and hence signal-receipt sensitivity varies in dependence on whether the terminal is put on a desk or is put in a user's pocket. For instance, if the terminal is put in a user's bag, the terminal could not have sufficient signal-receipt sensitivity.